Electrical sealed container



April 9,1935. c. J. WARNK E 1,996,845

ELECTRICAL SEALED GONTAIMFR Filed Oct. 31, 1931 Patented Apr. 9, 1935ELECTRICAL SEALED COIN'I'AIN'ER' Carl J. Warnke,'Elkhart, ind" assignor,by direct.

and mesne assignments, to The Adams &

Westlake Company, Chicago, 111., a corporation of Illinois ApplicationOctober 31, 1931, Serial No. 572,311

3 Claims.

My invention relates to electrical sealed containers, such as mercuryswitches, incandescent lamps of all types, radio tubes, rectifiers.mercury arc lamps, Roentgen tubes, power vacuum 5 tubes, and devices ofthis character generally in which an envelope of glass or vitreousmaterial encloses a sealed space having conductors disposed therein andelectrically communicating with an external power circuit throughlead-in conductors which are embedded in and through the wall of thecontainer, the disclosure in this application relating more particularlyto mercury switches as illustrating the advantages of my container.

One object of my invention is to devise a vitreous container forelectrical apparatus which is characterized by a high electricalresistance, an improved stability which makes the container moreresistant to the deteriorating effects of age than the glasses nowcommonly used for such purposes, and in which the constituents of theglass comprising the container have been so selected and arranged as toprovide for a substantially neutral glass through the balanced relationof the component substances.

A further object is to provide a container of the character indicated inwhich the percentage composition of the substances employed may bevaried over a definite range for the purpose of adjusting thecoeflicient of thermal expansion of the completed container in order tomeet the requirements of any particular operating con dition, withoutsacrificing the advantages of the container in other respects.

A further object is to provide a mercury switch having an envelope whichis composed of a-glass characterized by a melting point which issufficiently low to permit an easy working of the glass, and a lowcoeflicient of thermal expansion relative to the lamp glass now used inthe industry, and which is therefore capable of withstanding the ravagesof the electric are that occurs when the circuit is completed or brokenwithin the switch container.

A further object is to provide for a mercury switcher other types ofelectrical apparatus an envelope of the character indicated consistingof a glass which is substantially void of those materials, such as lead,tin, antimony and substances generally, which are decomposed under v andby the action of the electric arc and are A further object is to producea glass for electrical sealed containers which is substantially void ofany oxides which are reducible by hydrogen and is thereiore' superior tothe so-called alkaline glasses in this respect.

A further and more particular object is the employement of a glass thatmay be classed generally as a'magnesium silicate glass which, inaddition to the several advantages'noted above, is characterized by hightensile strength and toughness, a higher degree of resiliency than thelime glasses, ability to withstand and be substantially unafiected byrapid temperature fluctuations over wide ranges; and which, when used asthe envelope of a mercury switch, facilitates the free rolling of themercury mass, since there is no tendency on the part of the mercury toadhere to the container surface.

A further object is .to provide. a container formed of a glass which ischaracterized by a capacity for establishing a close aflinity withlead-in conductors, such as tantalum and molybdenum, when the materialof the container is in a plastic or partially liquid condition and aftercooling, to thereby effect a thorough wetting of the conductor surfaceand the creation of a tightseal therewith.

For the purpose of more particularly illustrating the details andadvantages of my invention, the same will be illustrated and describedas embodied in a mercury switch, but it will be understood that theinvention is considered generically applicable to other types ofelectrical apparatus in which sealed containers are employed.

Mercury switches are generally in the-form of glass containers which maybe filled with gases such as nitrogen, hydrogen, or carbon-monoxide forthe purpose of assisting in the dissipation of heat created by theelectric arc, and within which container rides a mass of mercury forbridging the space between a pair 01' electrodes disposed within thecontainer and connected by means of lead-in conductors passing throughthe wall of the envelope with an external. source of electricity. Bytilting the container in one direction, the body of mercury moves intoelectrical conducting relation with the electrodes and by moving thecontainer in the opposite direction, the body of mercury flows away fromone or both of the electrodes to break the circuit. Other modificationsof this construction may include an arrangement in which a mercury tomercury contact is effected between separated pools of mercury bytilting the container to cause a portion of the mercury to flow betweenthese pools. However constructed, switches of this character have beensubject to many operating disadvantages, particularly where used incircuits bearing currents of considerable ampere strength and which areintended to make and break the circuit a large number of times over aconsiderable period.

When the electrical circuit is interrupted or is about to be completedas above described. the tendency of the current to break down thedielectric strength of the intervening air gap results in the creationof an electric arc of relatively high temperature which has a markedcapacity for effecting deterioration of the switch. Glasses-which haveheretofore been employed in the making of switch envelopes havegenerally been characterized by a relatively high coeiiicient of thermalexpansion and a low melting point, so that the impingement of theelectric are upon the glass of the envelope in the region adjacent therupture of the electrical circuit frequently results in a breakdown ofthe glass at the indicated point, or close to the locality where thelead-in conductors are sealed in and through the envelope. Thiscondition is particularly aggravated where a mercury switch is employedin an inductive circuit owing to the high voltage are which is inducedat the breaking of the circuit and the resulting rapid changes oftemperature which subsequently obtain within the switch envelope. Thisrise in temperature occurs within a relatively short period of time, asdoes the temperature recession downwardly therefrom to the normaltemperature of the switch, so that the glass envelope is subjected to ahighly destructive efiect in both instances, the glass being actuallyeroded with a consequent decrease in the wall thickness and excessivestresses being thereby established in the envelope which are in additionto and superimposed on the natural stresses present in the glass. Theglass accordingly breaks at the indicated point and the switch istherefore removed from service. Similar rapid and temperature changesoccur in such switches when employed in circuits subject to high currentsurges, that is, in inductive circuits through which the current flowsintermittently and in which the loads are heavy, such as the lamp banksof advertising signs and similar installations. In both of the foregoinginstances, mercury switches as now known are prone toearly failure inservice owing to the deterioration and subsequent destruction of theglass envelope.

Other objections to glass envelopes as now used in mercury switchesarise from the fact that the type of glass employed frequently embodiesmetallic substances, reducible oxides, or materials generally which, inthe operation of the switch are decomposed by the high voltage arc, andare picked up by or amalgamate with the mercury. This decomposition ofwhat, so far as the desired efllclent operation of the switch isconcerned, are substantially in the nature of impurities, results in alessening of the purified condition of the mercury with a consequentaifecting of its capacity for operating according to its primarypurpose, or it may result in the formation of slag or film deposits onthe interior surface of the envelope, or between the electrodesthemselves, thus short-circuiting the switch.

As specific examples of the practice of the prior art'in the use ofsealed containers for electrical apparatus, and more particularlymercury switches, it may be noted that it has been heretofore proposedto utilize the so-called hard glasses I in connection with tungstenlead-in wires. Where such a container is formed of a lead borosilicateglass, it has been ascertained that, while the tungsten lead-in wiresmay be readily sealed through this glass owing to the closeness in thenumerical values of the coefficients of thermal expansion, the glasscontainer will not withstand severe usage over long periods. As onesolution of this particular difliculty, a bore-silicate glasscontainingan appreciable quantity of aluminum has been substituted for the leadbore-silicate glass, the former being the so-cailed pyrex glass, but theuse of this particular glass requires the employment of a fusion zone oflead hero-silicate glass, through which the tungsten lead-in wires maybe sealed, the lead glass being in turn united to the pyrex container.However, this fusion zone creates a region of weakness which is verysusceptible to cracking with a result that the hermetic condition of theenvelope is destroyed. Other modifications have contemplated the use ofa quartz container, but this type of envelope is subject to the samedisadvantages as discussed in connection with the pyrex container and toa greater degree. Still other attempts involved the employment ofenvelopes of relatively soft glass, but utilizing a protective elementof arcresisting material which is supported in some manner within thecontainer and out of contact therewith.

The principal object of the present invention is to overcome theforegoing disadvantages insofar as may be accomplished through changesin the character of the glass employed for the switch container and inthe adoption of a metal which will operate satisfactorily as a lead-inconductor with particular reference to its capacity for establishing agas-tight seal with the glass and in the maintenance of this sealthroughout the working range of the switch, considered from thestandpoint of temperature and the conductance of the electric current.For .this purpose, I have discovered that magnesium silicate glass, whenmade according to a'deflnite composition, possesses certain propertiesthat are particularly useful under the special conditions found inmercury switch operation, and is generally advantageous for use in avariety of sealed containers for electrical apparatus. The outstandingcharacteristic of this glass is the balanced relation of its componentparts, resulting in the formation of a glass which is substantiallyneutral or perhaps very slightly basic, as contrasted with the alkalinecharacteristics of the lime and soda potash glasses, and the acidproperties of the well known bore-silicate glasses, whose disadvantageshave already been discussed. In composition, my improved glass isconstituted of silicon dioxide (S102), magnesium oxide (MgO), boricoxide (8:03) and sodium oxide (Na-.0).

I have ascertained that, when these substances are combined in certaindefinite percentages and within a given range, the resulting glass isnot only substantially neutral or perhaps slightly basic, but ischaracterized by a high electrical resistance, a melting point which issufllciently low to permit the glass to be easily worked, toughness,capacity for withstanding shock, a high degree of heat resistance, asubstantial freedom from lead, tin, antimony, or substances which are decomposed by the action of the electric arc, and is also substantiallyvoid of any reducible oxide in an atmosphere of hydrogen. In addition,this glass is stable, more resistant to age, does not shattereasily,and, as will presently be discussed, is capacitated for establishing aremarkably close amnity with lead-in wires, suchas tantalum andmolybdenum. In the preferred composition, the

percentage of silicon dioxide may range from 68- to 71%, the amount ofmagnesium oxide employed varies from 10 to 14%, boric oxide from by theminimum coeflicient of thermal expansion which is approximately of theorder of from 48 to 54- x-l0-, while the utilization of a 68% portion ofsilicon dioxide will produce a glass having the maximum coeflicient ofthermal expansion, being approximately of the order'of from 58 to 64 x10 As lead-in conductors for the foregoing kind of glass, it has beenascertained-that wire composed of tantalum 'of molybdenum -works verysatisfactorily, owing to the capacity of these metals for being readilywetted by the glass and to maintain the seal thus obtained throughoutthe working temperature range of the container. For example, in thesealing of the above lead-in wires, it is believed that the acid oxideformed is substantially. dissolved in and by the glass while the latteris in a liquid,molten, or a semi-molten condition, thereby causing avery pronounced wetting action betweenthe glass and wire and,

resulting in an exceptionally tight seal. The strength of this seal isattested by the fact that there is no sharp dividing line between theleadin wire and the glass container, but that the seal is characterizedby a graded nature and composed of the glass, the metal oxide, and themetal proper. The relation between the wetting characteristics of thetantalum and molybdenum erence being had to the accompanying drawing,

and the novel means by which said objects are efiectuated will bedefinitely pointed out in the claims.

In the drawing, the figure represents a longitudinal, sectionalelevation of a. conventional form of mercury switch arranged incircuitbreaking position. J

The switch shown in the drawing is intended merely as illustrative ofswitches of this general character, and no claim is made thereto asregards the structural details of the switch, except to the extent asindicated more particularly hereinafter. sealed container l0 which isformed of magnesium silicate glass having the characteristics andcomposition noted above, and throughvthe walls of which pass lead-inconductors Ii and i2, composed of tantalum or molybdenum, which areconnected externally of the container to any suitable source ofelectricity by means of con- Speciflcally, the switch comprises a.

tainer III, the lead-in conductors ll and- 12'- are connectedrespectively to electrodes and I8 which may be of any de'siredshape andmaterial and bear any desired space relation to each other. The detailsof construction of the elements above described form no part of thepresent invention, except as regards the materials constituting thecontainer l0 and the lead-in conductors. i i and i2, so that they may bearranged for the carriage of currents of any value and atany voltageover any desired period of time, the sealing of the lead-in conductors Hand i2 withinth'e'walls of the container ill being such as to preventleakage at these points. In the drawing, the numeral I1 is intended todesignate the graded character of seal which obtains between the lead-inconductors and the material of the envelope.- The container III alsoencloses a body of mercury l8 which is shifted from end to endthereof-iassaid conductor is tilted by any approved means, the positionof said mercury in the drawing indicating a circuit-breaking positionand when said container is tilted in the opposite direction, the mercuryl8 rolls along the bottom of said container to bridge the space betweenthe electrodes iii and IE to thereby complete the circuitwithin theswitch. At the time the switch is made, the air content originallywithin the container I0 may be evacuated and a predetermined quantity iof a heat dissipating and are suppressing gas, such ashydrogen, may beinserted therein at some approved pressure.

The outstanding characteristics of, a mercury switch constructed asabove described, or, of any electrical apparatus which employs acontainer composed of the material set forth above,.is its abilitytowithstand hard usage. over extended periods of time without having itsprimary effectiveness continuously decreased andits capacity forremaining positively neutral so far as any tendency to promote anydeteriorating action in the other parts of the switch. Accordingly, theswitch is featured by a high degree of dependability and desirabilityfor use under conditions which are not satisfactorily met by presenttype switches. The composition of my improved glass is sufficientlyelastic to permit of any desired variations within the limits'outlinedin order to secure a type of glass which will best suit operatingconditions and with particular reference to any peculiar characteristicswhich the container should embody in order to satisfactorily meet theindicated condition, as regards coeflicient of thermal expansion,electrical resistance, toughness, nieltingpoint, and other factors.

While I have shown one set of combinations and elements thereof forefiectuating my. im-

proved sealed container, it will be understood that the same is intendedfor purpose of illustration only and in no wise to restrict the deviceto the exact forms and structures shown, for many changes may be madetherein without departing from the spirit of my invention.

I claim:

1. A glass for use in mercury switches and the like composed of silicain excess of 68%, magnesia in the next largest proportion, and an oxideof an alkali metal to the extent of at least 7%, said glass beingsubstantially free of lead, tin, antimony, and the like, and having acoeflicient of thermal expansion of 64 x 10- or less.

2. A glassfor use in mercury switches and the like composed of silica inexcess of 68%, magnesia in the next largest proportion, and an oxide ofan alkali metal to the extent of at least 7%, said glass beingsubstantially free of lead, tln,'antlmany, and the like, and having acoefllclent or thermal exnanslon 01' 64 x 10- or less, and a tantalum ormolybdenum conductor sealed therein. I 3. A glass for use in mercuryswitches and the like composed of silica in excess of 68%, magnesia inthe next largest proportion, and an oxide of an alkali metal to theextent-of atleast 7%, said glass being substantially neutral to basicand having a coefllcient of thermal expansion of 5 64 x 10- or less.CARL J. WARNKE.

